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Date: Thu, 12 Jul 2018 18:30:57 +0200
From: Szabolcs Nagy <nsz@...t70.net>
To: Dhiraj <mortalfw@...il.com>
Cc: musl@...ts.openwall.com
Subject: Re: overflow() at stdlib.h

* Dhiraj <mortalfw@...il.com> [2018-07-12 21:21:38 +0530]:
> Thanks Szabolcs for taking look into this,
> 
> > But over here uv__fs_pathmax_size() nor pathconf(path, _PC_PATH_MAX) is
> > used.
> >
> 
> > where?
> 
> In stdlib.h file.
> 

i don't understand what is the issue.

> However, we can allocate a "PATH_MAX + 1" or POSIX.1-2008 would allow us to
> pass in a NULL poiter and have realpath allocating enough memory.
> 

why +1?

PATH_MAX is the maximum amount of bytes realpath may write (i.e. it includes
the terminating nul byte).

> On Thu, Jul 12, 2018 at 9:12 PM, Szabolcs Nagy <nsz@...t70.net> wrote:
> > * m0rtal f!w <mortalfw@...il.com> [2018-07-12 19:55:56 +0530]:
> > > Team,
> > >
> > > File: stdlib.h#L:113
> > >
> > > i.e
> > > char *realpath (const char *__restrict, char *__restrict);
> > >
> > > According to the documentation of realpath() the output buffer needs to
> > be
> > > at least of size PATH_MAX specifying output buffers large enough to
> > handle
> > > the maximum-size possible result from path manipulation functions. (In
> > that
> > > instance, buf's size comes from uv__fs_pathmax_size(). That function
> > > attempts to use pathconf(path, _PC_PATH_MAX) as noted in the realpath(3)
> > > docs)
> > >
> >
> > sounds like a portability bug in uv__fs_pathmax_size()
> >
> > http://pubs.opengroup.org/onlinepubs/9699919799/functions/realpath.html
> >
> > it should use PATH_MAX if defined or null pointer if not
> > to be portable to posix conforming targets.
> >
> > > But over here uv__fs_pathmax_size() nor pathconf(path, _PC_PATH_MAX) is
> > > used.
> > >
> >
> > where?
> >
> > > Passing an inadequately-sized output buffer to a path manipulation
> > function
> > > can result in a buffer overflow. Such functions include realpath()
> > > readlink() PathAppend() and others.
> > >
> > > Request team to have a look and validate.
> > >
> > >
> > > Thank you
> >

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